1. Field of the Invention
The present invention relates to a roller provided rotatably on an arched roller shaft. More specifically, the invention relates to a roller which adapts the force tending to extend a sheet-shaped article in its cross-wise direction to act on the article passed thereover.
2. Statement of Prior Art
Conventionally, a roll having wrinkle stretching function or a wrinkling prevention function is shown in FIG. 7A. The known roll R4 has a roller 2d, whose external circumference increases progressively from the central part towards each end, and which is rotatably provided on the straight roller shaft 1d. Nevertheless, such a drum-shaped roll has a disadvantage wherein, if the article S to be passed by the roller 2d makes a wide contact (Sa part) with the roller 2d, the article S may be distorted and given a permanent set. Further, if the difference between the external circumference around the central part of the roller 2d and that around the opposite end parts thereof is increased to increase the force extending the article S in its cross-wide direction, there is difficulty in causing the article S to travel in a stable manner.
On the other hand, as shown in FIG. 7B, the roll R5 wherein the roller 2e has a constant sectional area and is rotatably provided on a curved or arched roller shaft 1e has been also known. As shown in FIG. 7C, if the article S is passed from the concave side of the roller shaft 1e to the convex side, then a force extending the article S in its cross-wise direction acts on the article. Nevertheless, if the degree of curvature of the roll is enlarged in order that the force of extending be increased, then the article may be given a large permanent set and also there is a difficulty in causing the article to travel in a stable manner.
For this reason, Conventionally, any of the aforementioned rolls can only be used with an extremely soft material such as plastic film, without giving rise to wrinkles.